From chessboard tweed to chessboard nanowire structure during pseudospinodal decomposition.

Microstructure evolution in complex nonlinear systems is of great interest from both scientific and engineering viewpoints. Here, we consider an important case of such an evolution, a coherent decomposition of a homogeneous parent phase involving the symmetry-lifting crystal lattice rearrangement of the product phase. It is shown that under certain conditions the transformation develops as a pseudospinodal decomposition, which is defined as a transformation with continuous changes of the compositions of both decomposed phases towards their equilibrium values. The pseudospinodal decomposition starts by the formation of a nanodomain precursor state with a so-called tweed structure. The three-dimensional modelling demonstrates that this tweed structure has an underlying chessboard feature, and this arrangement is a template for the further microstructure development that eventually produces a coherent two-phase chessboard nanowire pattern. The proposed theory and modelling describe the mechanism of the pseudospinodal decomposition and predict all observed three-dimensional features of the chessboard structure.